1. Field of the Invention
The present invention relates to a lens system, and more particularly to a zoom lens system which is suitable for used in the digital products.
2. Description of the Prior Art
So far, the lens system used in DC (digital camera) with a zoom ratio of three times is generally a three-group type lens system which is widely used, such as the zoom lens systems disclosed in JP Publication Nos 2000-267009, 2005-037727, 2005-070696 and 2007-079326, and these conventional zoom lens systems comprises, from the object side: a first lens group with a negative refractive power, a second lens group with a positive refractive power, and a third lens group with a positive refractive power. The first, second and third groups of lens elements move along the optical axis to accomplish zooming. After further study, we found that the above conventional lens systems still have the following problems:
JP Publication Nos 2000-267009 and 2005-037727 aim at low price, therefore, the lens elements used are plastic, and the desired zoom ratio is achieved. This is the style adopted by the canister style camera. When in use, the lens element protrudes outward, which leads to the problem of waterproof and falling off. Therefore, it will be a problem if these types of lens systems are used in cell phone or mobile machine.
The zoom lens system of JP Publication No 2005-070696 is additionally provided with a glass cover at the front end thereof, if it is used in the cell phone and if the lens system is too long, the lens system of the cell phone must be miniaturized.
The zoom lens system of JP Publication No 2007-079326 sequentially comprises, from the object side to the image side, a first lens group with a negative refractive power, a second lens group with a negative refractive power, a third lens group with a positive refractive power, and a fourth lens group with a positive refractive power. The first lens group is fixed, when zooming, the second, third and fourth lens groups move along the optical axis to realize zooming function. The first lens group is a right-angle prism at the optical path, the second lens group includes two concave lens elements and a meniscus lens element with a convex surface facing the object side. The third lens group includes two convex lens elements, a meniscus lens element with a convex object-side surface and a meniscus lens element with a convex object-side surface. The fourth lens group is a meniscus lens element with a concave surface facing the object side. The configuration of the prism facilitates the objective of miniaturization, however, the resultant zoom ratio is only 2.5 times, and the distortion aberration is also a big problem.
To solve the above problems, the inventor of the invention, based on the experiences and technology accumulated in the lens system researching field, invented a zoom lens system suitable for use in digital product.